$ \left(\dfrac{1}{81}\right)^{-\frac{1}{2}}$
$= 81^{\frac{1}{2}}$ To simplify $81^{\frac{1}{2}}$ , figure out what goes in the blank: $\left(? \right)^{2}=81$ To simplify $81^{\frac{1}{2}}$ , figure out what goes in the blank: $\left({9}\right)^{2}=81$ so $ 81^{\frac{1}{2}}=9$